In a traditional most popular process for producing tofu, tofu is produced by adding a nigari-type coagulant to soybean milk and filling the resultant mixture into a frame. In addition to conventional nigari (bittern) extracted from sea water, alkaline earth metal chlorides such as calcium chloride, magnesium chloride and the like can be used as a nigari-type coagulant, and the resultant nigari-tofu product is excellent in flavor, taste and texture in comparison with a tofu product produced by using a sulfate-type coagulant whose main component is alkaline earth metal sulfates. However, since a nigari-type coagulant has higher water-solubility and higher reactivity, there are many restrictions for using it. Then, in some cases, a delayed action coagulant prepared by covering nigari with a hydrogenated oil or an oil phase has been used.
On the other hand, for producing frozen tofu, starches, saccharides, gelatin, thickening polysaccharides, etc. are used to prevent freezing denaturation. However, when they are added to soybean milk, in many cases, soybean milk is thickened and a coagulant is hardly dispersed therein at a temperature at which the coagulant is allowed to react. Then, the addition of a coagulant is conducted after once cooling soybean milk to which a thickening raw material such as starch or the like has been added. However, there is such a problem that, when the temperature is raised again to cause coagulation, it is difficult to make best use of the original effects of nigari on flavor and tissue, and workability is also insufficient.